Some of part mounting facilities are known as implementing an assembly method to complete a single assembly or product (hereinafter referred to as “workpiece” by a particular number (a single or plural) of human operators during one cycle of operation (i.e., cell production system), as disclosed, for example, in Patent Document 1. According to such part mounting facilities, the particular number of human operators moves along with the workpiece and complete a part mounting operation while the workpiece moves over one-cycle distance.
However, the part mounting facility disclosed in Patent Document 1 may encounter a problem that as to a workpiece having a large number of part items to be mounted, working loads on the human operators increase too much due to an increase in work mastering man-hours. Furthermore, an undue increase in the working loads will hinder the human operators from performing a highly efficient mounting operation.